The Missoula City-County Air Pollution Control Program's Chapter X, Variances, which was adopted by the Montana Board of Health and Environmental Sciences on June 28, 1991 and submitted by the Governor of Montana to EPA in a letter dated August 20, 1991, is disapproved. This rule is inconsistent with section 110(i) of the Clean Air Act, which prohibits any State or EPA from granting a variance from any requirement of an applicable implementation plan with respect to a stationary source.